Properties of GaN layers deposited on (0001) sapphire templates

High temperature gallium nitride (HT-GaN) layers were grown by HVPE (hydride vapor phase epitaxy) on low temperature GaN (LT-GaN) nucleation layers deposited by HVPE. The (0001) sapphire substrates were used. The LT-GaN process parameters were as follows: HCl flow rate was 10 sccm/min, temperature 450degC and deposition time intervals 7 and 9 minutes for sample #1 and #2, respectively. The values were chosen after previous optimization of this stage of technology. Before nucleation layer deposition sapphire substrates were pre-heated for 10 min in the N2:NH3 ambient. The nucleation layer epitaxy was followed by recrystallization and migration process for 10 minutes. Morphologies of LT- and HT-GaN layers were examined by scanning electron microscopy. Properties of HT-GaN layers were investigated by photoluminescence spectra and micro-Raman measurements.